U.S. Pat. No. 3,581,733 describes a system for continuously monitoring blood pressure within blood vessels and the heart. The system includes a catheter joined to a connecting tube leading to a pressure transducer that converts physical pressure signals into an electrical impulse which is then fed to a recording machine, such as an oscilloscope. As pressure readings can be seriously affected if blood should coagulate in any part of the pressure monitoring system, this patent describes continuously forcing a very slow flow of a physiological salt solution (normal saline would be an example) into the patient. This very slow flow rate is sufficient to prevent blood from backing up into the catheter and connecting tube, but is so slow that it does not cause any significant error in blood pressure reading.
Immediately after connecting the system to the patient and periodically through pressure monitoring, it becomes necessary to flush a larger amount of parenteral liquid into the patient, particularly to insure that the catheter or needle is completely free of blood. U.S. Pat. No. 3,581,733 does this flushing by a valve 18. Another type flushing valve is described in Pat. No. 3,675,891. The flushing valve therein has an elongated stem that must be pulled to actuate the valve. If the valve is not physically anchored to a rigid IV pole, transducer, etc., this operation requires two hands; i.e., one to hold the valve and one to pull the stem. Should the stem ever break off during the pulling action, the valve would be rendered useless. In addition, the valve of U.S. Pat. No. 3,675,891 includes a very large number of complicated parts including special sealing gaskets, etc.